Cryogen pressure vessel assembly for superconducting magnets

ABSTRACT

A cryogen pressure vessel assembly for a superconducting magnet comprises an inner former, an outer former, and an outer shell. The inner former has a plurality of superconducting magnet coils wound thereon, and the outer former has a plurality of bucking coils wound thereon. The inner former, the outer former, and the outer shell form a fluid boundary for a cryogen. In one aspect, a pressure face is formed on at least one of the coil formers, and a radial slot for receiving wires entering and exiting a coil is disposed in the pressure face. A plurality of wire clamps are positioned in the radial slot, with each wire clamp in the plurality of wire clamps including: a front face extending coplanar with the pressure face, a rear face opposite the front face, the rear face contacting a back surface of the radial slot, and a recess formed in the rear face, the recess forming a channel for passage of the wires.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of a priority under 35 U.S.C. 119 toGreat Britain Patent Application No. 0227226.8 filed Nov. 21, 2002, theentire contents of which are hereby incorporated by reference.

BACKGROUND OF INVENTION

This invention relates to superconducting magnets. More particularly,the invention relates to cryogen pressure vessel assemblies forsuperconducting magnets.

As is well known, a coiled magnet, if wound with wire possessing certaincharacteristics, can be made superconducting by placing it in anextremely cold environment, such as by enclosing it in a cryostat orpressure vessel containing liquid helium or other cryogen. The extremecold reduces the resistance in the magnet coils to negligible levels,such that when a power source is initially connected to the coil tointroduce a current flow through the coils, the current will continue toflow through the coils due to the negligible resistance even after poweris removed, thereby maintaining a magnetic field. Superconductingmagnets find wide application, for example, in the field of magneticresonance imaging (hereinafter “MRI”).

A typical superconducting magnet assembly for use in MRI consists of twosets of superconducting coils disposed in a cryogen vessel. An inner setof coils, usually called the main magnet coils, produce a uniformmagnetic field of large magnitude in an imaging volume. The conventionalcryogen pressure vessel is a circular, cylindrical drum in which aliquid cryogen, such as helium, is maintained under pressure. The maincoils are wound separately around coil formers, also known as spools orbobbins, placed in grooves machined in the drum and spaced axially alongthe inside of the drum. Another set of outer magnet coils, known asbucking coils, are spaced from and surround the main coils, and aresupported by a structure secured to the drum. The bucking coils carrycurrents in the direction opposite to the direction of currents beingcarried by the main coils so as to cancel the stray magnetic fieldoutside the magnet.

An example of an MRI system including a superconducting magnet assemblyis described in European Patent No. EP 0 587 423. As shown in FIG. 1,the magnet assembly includes a superconducting main magnet field coilassembly 10 which generates a substantially uniform magnetic fieldlongitudinally through an examination region 12. A gradient magneticfield coil assembly 14 selectively creates gradient magnetic fieldsacross the examination region 12. A gradient magnetic field controlmeans 16 controls a current pulse generator 18 to apply current pulseswith selected characteristics to the gradient field coils to cause thedesired magnetic field pulse to be generated.

A resonance excitation and manipulation means includes a radio frequencytransmitter 20 for generating radio frequency pulses of the appropriatefrequency and spectrum for inducing resonance of selected dipoles in theexamination region 12. The radio frequency transmitter is connected witha radio frequency antenna 22 disposed surrounding the examination regionand inside the gradient magnetic field coil assembly 14. The RF coiltransmits radio frequency pulses into the region of interest andreceives radio frequency resonance signals emanating therefrom.Alternatively, a separate receiving coil may be provided. The receivedmagnetic resonance signals are conveyed to a digital radio frequencyreceiver 24 for demodulation. The demodulated, digital radio frequencysignals are reconstructed into a magnetic resonance image representationby an array processor or other image reconstruction means 26. Thereconstructed image representation is stored in an image memory 28. Theimage representation may be displayed on a video monitor 30, subject tofurther processing, stored on tape or disk, or the like.

The superconducting magnet assembly 10 includes an outer vacuum vessel40 which defines an inner, cylindrical room temperature bore 42 withinwhich the gradient field coil assembly 14 is received. A series ofsuperconducting, annular magnetic coils 44 are mounted on a coil former46 and disposed within an annular cryogen pressure vessel 48. A port 50permits the cryogen pressure vessel 48 to be maintained filled withliquid helium or the like as it evaporates to hold the temperaturewithin the pressure vessel at about 4.2° K. Preferably, a heliumrecovery and recondensing system (not shown) is interconnected with theport 50. Also disposed within the cryogen pressure vessel 48 is abucking coil assembly 56, which is mounted around the exterior of thesuperconducting magnet coils 44 and connected electrically in seriestherewith. The bucking coil assembly 56 generates a magnetic field whichopposes the fields generated by the main magnets 44 in the exterior ofthe cryostat, while producing a strong uniform magnetic field along thebore 42. The bucking coil assembly comprises magnetic coils 58 woundaround a coil former 62. The cryogen pressure vessel 48 is surrounded bya first cold shield 52 which is cooled to about 200 K. or less. A secondcold shield assembly 54, which is chilled to about 60°-70° K. or less,is disposed between the inner cold shield assembly and the vacuum vessel40. In this way, a series of thermal gradations are maintained tominimize the evaporation of the cryogen.

There are many factors that challenge the designer of a superconductingmagnet assembly. First, the assembly is subject to many stresses. Forexample, in the process of energizing the magnets, the coils and coilformer are subjected to significant electromagnetic loading. In theprocess of cooling the coils to superconductive temperatures, unevencooling rates and the use of a mix of materials in the coil former cancause differential expansion in the coils and coil former, which createsstresses in the coils and coil former. The relief these stresses cancause the sudden movement of the coils, which is a major cause ofquenches (rapid loss of superconductivity and collapse of magnet field)in the magnets. In addition, relative movement of coils as a result ofsmall changes in ambient temperature or pressure can also causeinhomogeneity in the magnet. Second, space is at a premium, with manymodern designs aiming to make the magnet as small as possible. These andmany other factors combine to make the design of a superconductingmagnet assembly very challenging.

SUMMARY OF INVENTION

The above-described deficiencies are overcome or alleviated by a cryogenpressure vessel assembly for a superconducting magnet, the assemblycomprising an inner former, an outer former, and an outer shell. Theinner former has a plurality of superconducting magnet coils woundthereon, and includes a first pair of end walls extending therefrom. Theouter former has a plurality of bucking coils wound thereon and a secondpair of end walls extending therefrom. The outer former extends betweenthe first pair of end walls, and the outer shell extends between thesecond pair of end walls. The inner former, the outer former, the firstpair of end walls, the second pair of end walls, and the outer shellform a fluid boundary for the cryogen.

In one aspect, a pressure face is formed on at least one of the coilformers, and a radial slot for receiving wires entering and exiting thecoil is disposed in the pressure face. A plurality of wire clamps arepositioned in the radial slot, with each wire clamp in the plurality ofwire clamps including: a front face extending coplanar with the pressureface, a rear face opposite the front face, the rear face contacting aback surface of the radial slot, and a recess formed in the rear face,the recess forming a channel for passage of the wires entering andexiting the coil. In another aspect, first and second arcuate slots arein communication with the recess. The first and second arcuate slots aresized to accept a single wire forming a portion of the coil.

The above discussed and other features and advantages of the presentinvention will be appreciated and understood by those skilled in the artfrom the following detailed description and drawings.

BRIEF DESCRIPTION OF DRAWINGS

Referring to the exemplary drawings wherein like elements are numberedalike in the several FIGS.:

FIG. 1 is a schematic diagram of a magnetic resonance imaging systemincluding a superconducting magnet assembly;

FIG. 2 is a perspective view of a cryogen pressure vessel assembly;

FIG. 3 is a cross-sectional view of the cryogen pressure vessel takenalong 3—3 in FIG. 2;

FIG. 4 depicts a plurality of wire clamps disposed within a slot formedin a magnet former;

FIG. 5 is a top perspective view of a wire clamp of FIG. 4;

FIG. 6 is an is a bottom perspective view of the wire clamp of FIG. 4;and

FIG. 7 is a back perspective view of the wire clamp of FIG. 4.

DETAILED DESCRIPTION

Referring to FIGS. 2 and 3, a cryogen pressure vessel is shown generallyat 100. Cryogen pressure vessel 100 may be used, for example, in placeof prior art cryogen pressure vessel 48 of FIG. 1. Cryogen pressurevessel 100 is a generally cylindrical structure formed from threeconcentric structures: an inner former 102 nested within an outer former104 and an outer shell 106. Inner former 102 includes a cylindricalshell 108 and end walls 112, which are positioned at the ends ofcylindrical shell 108 and extend radially outward about the perimeter ofthe cylindrical shell 108. Outer former 104 includes a cylindrical shell114, which extends between end walls 112. Outer former 104 also includesend walls 116, which extend radially outward about the perimeter of thecylindrical shell 114. Outer shell 106 is a cylindrical shell, whichextends between end walls 116.

Formed between the outside diameters of the end walls 112 and an insidediameter of cylindrical shell 114 are seams 120, and formed between theoutside diameters of the end walls 116 and an inside diameter of outershell 106 are seams 122. The seams 120 and 122 are joined using, forexample, welding, to create a sealed vessel in which liquid cryogen(e.g., liquid helium) may be contained. Cylindrical shells 108 and 116,end walls 112 and 116, and outer shell 106 form a fluid boundary for thecryogen.

As is shown in FIG. 3, inner former 102 includes a plurality of coilformer walls 150 that, along with cylindrical shell 108, form pocketsfor supporting superconducting magnet net coils 44. Coil former walls150 are disposed on the cylindrical shell 108 between the end walls 112,and extend radially outward about the perimeter of cylindrical shell108. Similarly, outer former 104 includes a plurality of coil formerwalls 152, which extend radially outward about the perimeter ofcylindrical shell 114. Bucking coils 58 are supported in pockets formedbetween coil former walls 152, end walls 116, and cylindrical shell 114.Various apertures 154 are disposed in cylindrical shell 114 and outershell 106 to allow passage of wiring for coils 44 and 58 and to allowfor evaporation of liquid cryogen.

As can be seen in FIG. 3, a portion of cylindrical shell 108 proximatesuperconducting coils 44 may have an increased thickness, as is neededto provide support to superconducting coils 44. Similarly, a portion ofcylindrical shell 114 proximate bucking coils 58 may have an increasedthickness, as is needed to provide support to bucking coils 58.

Inner former 102 may be machined from a single piece of material suchas, for example, stainless steel. Alternatively, inner former 102 may beformed from carbon fiber, fiberglass, or the like. Similarly, outerformer 104 may be machined from a single piece of material such as, forexample, stainless steel. Alternatively, outer former 104 may be formedfrom carbon fiber, fiberglass, or the like. Preferably, inner former102, outer former 104, and outer shell are constructed of the samematerial to reduce the possibility of differential expansion and,thereby reduce the possibility of sudden coil movement, which caninitiate quenches.

Cryogen pressure vessel 100 is assembled by winding coils 44 and 58directly onto inner former 102 and outer former 104, respectively. Theinner former 102 is then inserted within the outer former 104, and seam120 is welded. The inner and outer formers 102 and 104 are then insertedwithin the outer shell 106, and seam 122 is welded.

The present invention provides concentric cylinders 108 and 114 asintegral structural members of the cryogen vessel 100, and the coils 44and 58 are wound directly into pockets formed on these cylinders. Thisdesign makes use of an integral structure which serves as both the coilformer for winding coils 44 and 58, and as the pressure vesselcontaining the liquid cryogen. As the cylinders 108 and 114 are allconstructed of the same material, and as there are no bolted junctions,there is no possibility of sudden movements of the windings 44 and 58 toinitiate quenches. Thus, the present invention provides for a simple andstructurally efficient way to make a stiff cryogen vessel with nodifferential expansion of the coil formers and no possibility of suddenmovements of the coil formers with respect to each other. In addition,the need for separate coil formers is eliminated, saving valuable radialspace. The structure carries all the loads imposed by the winding of thecoils, the operating stress of the coils, and the mechanical stressesdue to the weight of the magnet and the suspension system.

Referring again to FIG. 3, each superconducting coil 44, 58 is mountedwithin the pockets formed by the coil former walls 150 and 152,respectively. As is known, each coil 44 and 58 comprises several partialcoils, resulting in many wires entering and leaving the pocket in whichthe coils 44 and 58 are formed. For example, there can be as many astwelve wires entering and exiting each coil 44 or 58. To allow the wiresto enter and exit the pocket, a radial slot 156 is disposed in one ormore of the coil former walls 150 and 152.

Referring now to FIG. 4, a section of a coil former wall 150 including aradial slot 156 is shown. In the embodiment of FIG. 4, the radial slot156 extends along the entire height of a pressure face 158 of the coilformer wall 150, from cylindrical shell 108 to the outside diameter ofcoil former wall 150. The pressure face 158 is the face of the coilformer wall 150 that faces the coil 44. A plurality of wires, 200, 201,and 202, which form a portion of coil 44 (FIG. 3) are disposed in radialslot 156. It will be recognized that while only three wires 200, 201,and 202 are shown for example, and that many additional wires may beneeded to form a coil 44.

Disposed within slot 156 is a pair of alignment pins 204, which are eachrigidly secured to cylindrical shell 108. Alignment pins 204 act toalign and secure a plurality of wire clamps 206 within radial slot 156.

Referring to FIGS. 5-7, various views of a wire clamp 206 are shown.Wire clamp 206 is a structure having a top face 210, a bottom face 212,a front face 214, a back face 216, and side faces 218. Extending fromtop face to bottom face, and positioned proximate side faces 218, are apair of apertures 219. Apertures 219 accept alignment pins 204 (FIG. 4).Disposed in back face 216, and extending from top face 210 to bottomface 212, is a generally u-shaped recess 220. A chamfer 222 is formedbetween u-shaped recess 220 and bottom face 212. Chamfers 224 are alsoformed between each side face 218 and end face 216.

Formed on bottom face 212 and extending from chamfer 222 to front face214 are two arcuate slots 226. As is shown in FIG. 5, each arcuate slot226 is sized to accept a single wire 228, with the arc of the slot beingconfigured to support a gradual bend of the wire. The arcs in each pairof arcuate slots 226 oppose each other such that the wires 228 disposedin slots 226 bend in opposite directions. The ends of slots 226proximate front face 214 are radiused to remove any sharp edges that maydamage the wires 228. The arcuate slots 226 may be dimensioned suchthat, when a wire 228 is captured between two adjacent wire clamps 206,the insulation of the wire is compressed in the arcuate slots 226,thereby holding the wire 228 tight and maintaining winding tension. Toensure that each wire 228 is electrically insulated from each other, thewire clamps 206 are preferably manufactured from an electricallyinsulative material.

Referring to FIGS. 4 and 5, the arrangement of wire clamps 206 withinslot 156 can now be described. Wire clamps 206 are positioned onalignment pins 204 in stacked relationship, with alignment pins 204extending through apertures 219 and opposing top and bottom faces 210and 212 of adjacent wire clamps 206 contacting each other. In thisconfiguration, the top face 210 of an adjacent wire clamp 206 acts toretain wires 228 within the arcuate slots 226.

The wire clamps 206 and radial slot 156 are dimensioned such that: thefront face 214 of each wire clamp 206 is aligned coplanar with thepressure face 158 of coil former wall 150; the back face 216 of eachwire clamp 206 contacts a rear surface 230 of the radial slot 156; andthe side faces 218 of each wire clamp 206 contact side surfaces 232 ofthe radial slot 156. When the wire clamps 206 are in position, theu-shaped recesses 220 of the wire clamps 206 form a passage for thewires (e.g., 200, 201, 202) along the rear surface 230 of the radialslot 156. The passage ensures that any pressure placed on the front face214 of the wire clamps 206 by the coils 44 will be translated to therear surface 230 of the radial slot 156, and will not damage the wires.This design allows a large area for routing wires in and out, whilematching the stiffness of the pressure face 158 with the strength of thewire clamps 206.

The chamfer 222 formed in each wire clamp 206 allows a wire (e.g., 201)to gradually bend away from the rear surface 230 of the radial slot 156so that it may be received in the arcuate slots 226. One of the arcuateslots 226 directs a wire 228 from the wire clamp 206 in a directiongenerally parallel to the front face 214 and pressure face 158. Afterthe wire is wrapped around the cylindrical shell 108 to form a partialcoil, the wire 228 is received in the other arcuate slot 226.

The wire clamps 206 serve to route wire radially in the pockets formedby coil former walls 150 and 152, introducing the wire into and out ofthe coil at the correct depth in the pocket. The wire clamps 206 alsoserve to hold the wire tight to maintain winding tension. In addition,the clamps 206 carry loads from the pressure face 158 to the back of theslot 230, thus preventing these loads from causing wire movement. Bypreventing wire movement, the wire clamps 206 prevent quenches in themagnets.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims. Moreover, the use of the terms first, second, etc. do not denoteany order or importance, but rather the terms first, second, etc. areused to distinguish one element from another.

1. A cryogen pressure vessel assembly for a superconducting magnet, thecryogen pressure vessel assembly comprising: an inner former having aplurality of superconducting magnet coils wound thereon, said innerformer including a first pair of end walls extending therefrom; an outerformer having a plurality of bucking coils wound thereon, said outerformer extending between said first pair of end walls and including asecond pair of end walls extending therefrom; an outer shell extendingbetween said second pair of end walls; and wherein said inner former,said outer former, said first pair of end walls, said second pair of endwalls, and said outer shell form a fluid boundary for a cryogen.
 2. Thecryogen pressure vessel assembly of claim 1, wherein said inner formerfurther includes: a first plurality of coil former walls extendingradially outward about a perimeter of said first shell, said firstplurality of coil former walls forming a plurality of pockets for saidplurality of superconducting magnet coils.
 3. The cryogen pressurevessel assembly of claim 2, further comprising: a second plurality ofcoil former walls extending radially outward about a perimeter of saidsecond shell, said second plurality of coil former walls forming aplurality of pockets for said plurality of bucking coils.
 4. The cryogenpressure vessel assembly of claim 2, said cryogen pressure vesselassembly further comprising: a pressure face formed on at least one coilformer wall in said plurality of coil former walls; a radial slotdisposed in said pressure face, said radial slot for receiving wiresentering and exiting a superconducting magnet coil; and a plurality ofwire clamps positioned in said radial slot, each wire clamp in saidplurality of wire clamps including: a front face extending coplanar withsaid pressure face, a rear face opposite said front face, said rear facecontacting a back surface of said radial slot, and a recess formed insaid rear face, said recess forming a channel for passage of said wiresentering and exiting said superconducting magnet coil.
 5. The cryogenpressure vessel assembly of claim 4, wherein each wire clamp in saidplurality of wire clamps further includes: first and second arcuateslots in communication with said recess, said first and second arcuateslots being sized to accept a single wire forming a portion of saidsuperconducting magnet coil.
 6. The cryogen pressure vessel assembly ofclaim 5, wherein each wire clamp in said plurality of wire clampsfurther includes: a chamfer extending between said recess and said firstand second arcuate slots.
 7. The cryogen pressure vessel assembly ofclaim 4, further comprising: alignment pins extending along said radialslot from said first shell, said plurality of wire clamps being disposedon said alignment pins.
 8. A cryogen pressure vessel assembly for asuperconducting magnet, the cryogen pressure vessel assembly comprising:a first cylindrical shell forming a first portion of a fluid boundaryfor a cryogen; a first pair of coil former walls extending radiallyoutward about a perimeter of said first cylindrical shell, said firstpair of coil former walls said first cylindrical shell forming a pocket;a superconducting magnet coil disposed in said pocket; a first pair ofend walls extending radially outward about said perimeter of said firstcylindrical shell, said first pair of coil former walls and saidsuperconducting magnet coil being positioned between said first pair ofend walls; a second cylindrical shell coaxial to said first cylindricalshell and extending between said first pair of end walls, said firstpair of end walls and said second cylindrical shell forming a secondportion of said fluid boundary for said cryogen; a second pair of coilformer walls extending radially outward about a perimeter of said secondcylindrical shell, said second pair of coil former walls forming atleast one pocket; and a bucking coil disposed in said at least onepocket.
 9. The cryogen pressure vessel assembly of claim 8, furthercomprising: a second pair of end walls extending radially outward abouta perimeter of said second cylindrical shell; and an third cylindricalshell coaxial to said first cylindrical shell and extending between saidsecond pair of end walls, said second pair of end walls and said thirdcylindrical shell forming a third portion of said fluid boundary forsaid cryogen.
 10. The cryogen pressure vessel assembly of claim 8, saidcryogen pressure vessel assembly further comprising: a pressure faceformed on at least one coil former wall in said first pair of coilformer walls, said pressure face contacting said superconducting magnetcoil; a radial slot disposed in said pressure face, said radial slot forreceiving wires entering and exiting said superconducting magnet coil,and a plurality of wire clamps positioned in said radial slot, each wireclamp in said plurality of wire clamps including: a front face extendingcoplaner with said pressure face, a rear face opposite said front face,said rear contacting a back surface of said radial slot, and a recessformed in said rear face, said recess forming a channel for passage ofsaid wires entering and exiting said superconducting magnet coil. 11.The cryogen pressure vessel assembly of claim 10, wherein each wireclamp in said plurality of wire clamps further includes: first andsecond arcuate slots in communication with said recess, said first andsecond arcuate slots being sized to accept a single wire forming aportion of said superconducting magnet coil.
 12. The cryogen pressurevessel assembly of claim 11, wherein each wire clamp in said pluralityof wire clamps further includes: a chamfer extending between said recessand said first and second arcuate slots.
 13. The cryogen pressure vesselassembly of claim 10, further comprising, alignment pins extending alongsaid radial slot from said first cylindrical shell, said plurality ofwire clamps being disposed on said alignment pins.
 14. A cryogenpressure vessel assembly for a superconducting magnet, the cryogenpressure vessel comprising: a coil former; a coil disposed on said coilformer; a pressure face formed on said coil former, said pressure facecontacting said coil; a radial slot disposed in said pressure face, saidradial slot for receiving wires entering and exiting said coil; and aplurality of wire clamps positioned in said radial slot, each wire clampin said plurality of wire clamps including: a front face extendingcoplanar with said pressure face, a rear face opposite said front face,said rear face contacting a back surface of said radial slot, and arecess formed in said rear face, said recess forming a channel forpassage of said wires entering and exiting said coil.
 15. The cryogenpressure vessel assembly of claim 14, wherein each wire clamp in saidplurality of wire clamps further includes: first and second arcuateslots in communication with said recess, said first and second arcuateslots being sized to accept a single wire forming a portion of saidcoil.
 16. The cryogen pressure vessel assembly of claim 15, wherein eachwire clamp in said plurality of wire clamps further includes: a chamferextending between said recess and said first and second arucate slots.17. The cryogen pressure vessel assembly of claim 14, furthercomprising: alignment pins extending along said radial slot, saidplurality of wire clamps being disposed on said alignment pins.
 18. Amethod of assembling a cryogen pressure vessel assembly, the methodcomprising: winding a plurality of superconducting magnet coils around afirst cylindrical shell, said first cylindrical shell including a firstpair of end walls extending radially outward about a perimeter of saidfirst cylindrical shell; winding a plurality of bucking coils around asecond cylindrical shell; inserting said first cylindrical shell withinsaid second cylindrical shell; joining a first seam formed between saidsecond cylindrical shell and outside diameters of said first pair of endwalls.
 19. The method of claim 18, wherein said second cylindrical shellincludes a second pair of end walls extending radially outward about aperimeter of said second cylindrical shell, said method furthercomprising: inserting said second cylindrical shell within a thirdcylindrical shell; and joining a second seam formed between said thirdcylindrical shell and outside diameters of said second pair of endwalls.
 20. The method of claim 19, wherein said joining said first seamand said joining said second seam each include welding said seams.
 21. Asuperconducting magnet assembly comprising: an outer vacuum vesseldefining an inner bore; and a cryogen pressure vessel disposed withinsaid outer vacuum vessel, said cryogen pressure vessel comprising: aninner former having a plurality of superconducting magnet coils woundthereon, said inner former including a first pair of end walls extendingtherefrom, an outer former having a plurality of bucking coils woundthereon, said outer former extending between said first pair of endwalls and including a second pair of end walls extending therefrom, anouter shell extending between said second pair of end walls, and whereinsaid inner former, said outer former, said first pair of end walls, saidsecond pair of end walls, and said outer shell form a fluid boundary toretain a cryogen within said cryogen pressure vessel.
 22. The cryogenpressure vessel assembly of claim 21, said cryogen pressure vesselassembly further comprising: a pressure face formed on said innerformer, said pressure face contacting said superconducting magnet coil;a radial slot disposed in said pressure face, said radial slot forreceiving wires entering and exiting a superconducting magnet coil; anda plurality of wire clamps positioned in said radial slot, each wireclamp in said plurality of wire clamps including: a front face extendingcoplanar with said pressure face. a rear face opposite said front face,said rear face contacting a back surface of said radial slot, and arecess formed in said rear face, said recess forming a channel forpassage of said wires entering and exiting said superconducting magnetcoil.
 23. The cryogen pressure vessel assembly of claim 22, wherein eachwire clamp in said plurality of wire clamps further includes: first andsecond arcuate slots in communication with said recess, said first andsecond arcuate slots being sized to accept a single wire forming aportion of said superconducting magnet coil.
 24. A magnetic resonanceimaging system comprising: a superconducting magnet assembly including:an outer vacuum vessel defining an inner bore, a cryogen pressure vesseldisposed within said outer vacuum vessel, said cryogen pressure vesselcomprising: an inner former having a plurality of superconducting magnetcoils wound thereon, said inner former including a first pair of endwalls extending therefrom, an outer former having a plurality of buckingcoils wound thereon, said outer former extending between said first pairof end walls and including a second pair of end walls extendingtherefrom, an outer shell extending between said second pair of endwalls, and wherein said inner former, said outer former, said first pairof end walls, said second pair of end walls, and said outer shell form afluid boundary to retain a cryogen within said cryogen pressure vessel;and a gradient magnetic field coil assembly disposed in said inner bore.25. The magnetic resonance imaging system of claim 24, wherein saidcryogen pressure vessel assembly further includes: a pressure faceformed on said inner former, said pressure face contacting saidsuperconducting magnet coil; a radial slot disposed in said pressureface, said radial slot for receiving wires entering and exiting asuperconducting magnet coil; and a plurality of wire clamps positionedin said radial slot, each wire clamp in said plurality of wire clampsincluding: a front face extending coplanar with said pressure face, arear face opposite said front face, said rear face contacting a backsurface of said radial slot, and a recess formed in said rear face, saidrecess forming a channel for passage of said wires entering and exitingsaid superconducting magnet coil.
 26. The magnetic resonance imagingsystem of claim 25, wherein each wire clamp in said plurality of wireclamps further includes: first and second arcuate slots in communicationwith said recess, said first and second arcuate slots being sized toaccept a single wire forming a portion of said superconducting magnetcoil.
 27. A magnetic resonance imaging system comprising: asuperconducting magnet assembly including: an outer vacuum vesseldefining an inner bore, a cryogen pressure vessel disposed within saidouter vacuum vessel, said cryogen pressure vessel comprising: a coilformer, a coil disposed on said coil former, a pressure face formed onsaid coil former, said pressure face contacting said coil, a radial slotdisposed in said pressure face, said radial slot for receiving wiresentering and exiting said coil, and a plurality of wire clampspositioned in said radial slot, each wire clamp in said plurality ofwire clamps including: a front face extending coplanar with saidpressure face, a rear face opposite said front face, said rear facecontacting a back surface of said radial slot, and a recess formed insaid rear face, said recess forming a channel for passage of said wiresentering and exiting said coil; and a gradient magnetic field coilassembly disposed in said inner bore.
 28. The magnetic resonance imagingsystem of claim 27, wherein each wire clamp in said plurality of wireclamps further includes: first and second arcuate slots in communicationwith said recess, said first and second arcuate slots being sized toaccept a single wire forming a portion of said coil.
 29. The magneticresonance imaging system of claim 28, wherein each wire clamp in saidplurality of wire clamps further includes: a chamfer extending betweensaid recess and said first and second arcuate slots.
 30. The magneticresonance imaging system of claim 29, further comprising: alignment pinsextending along said radial slot, said plurality of wire clamps beingdisposed on said alignment pins.